Vapor pressure control means



VAPOR PRESSURE CONTROL MEANS Filed July 25, 1931 2 Sheets-Sheet l Inventor Eugene H Reid.

His Aht orneg.

Oct. 1, 1935. H. REID VAPOR PRESSURE CONTROL MEANS Filed July 25, 1931 2 Sheets-Sheet 2 w m 1M W /I III P 1 C w I ////I/// m 0 1m 1 u e u a m c C o a o D V C 4000 5000 e000 1000 0000 D- C. Load Tan/r Dome Coils over- Cathode To Cathode 0 0 W W M M 0 M 9508 Lgmk 8 $3 8 Load Current Inventbr Eugene H. Reid 5 His Attorneg.

Patented Oct. 1, 1935 r UNlTED STATES VAPOR PRESSURE CONTROL IVIEAN S Eugene H. Reid, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application July 25, 1931, Serial No. 553,135

3 Claims.

My invention relates to apparatus for transmitting power between alternating and direct current circuits through a space discharge device such as a mercury arc rectifier or inverter and its principal object is the provision of an improved means for controlling the vapor pressure in such space charge device whereby the load capacity of the device is increased.

In the operation of mercury are devices particularly of high power it is of especial importance that the pressure of the vapor within the evacuated receptacle of the device be maintained constant at a predetermined value in all portions of the space within the evacuated receptacle. If this pressure is low the current which the vapor will carry is reduced; if on the other hand the pressure is too high danger of vapor breakdown arises. The mercury arc device operates, therefore, most efiiciently only within predetermined comparatively narrow limits of vapor pressure and of temperature, and it is desirable that the cooling means which must be provided to absorb the heat losses incident to operation be so arranged as to maintain the vapor pressure within these limits.

Difficulties have been encountered heretofore, however, especially in certain high capacity mercury arc devices, in the control and equalization of vapor pressure in different portions of the space within the evacuated receptacle, these difficulties being due to the fact that in certain portions of this space appreciably more heat loss must be absorbed by the cooling means per unit space than in other portions, the cooling means as a whole thus being required to be distributed in such manner as to absorb much greater heat loss in these certain portions of the space within the device than in other portions.

In order to maintain the vapor pressure within the required narrow limits it is necessary not only that sufficient cooling and condensing surface be provided to absorb the total heat losses from the vapor but that a substantially increased amount of condensing surface per unit space be provided in those regions of the evacuated space within which the cooling and condensing means are most effective in the control of vapor pressure. It follows that in the usual mercury arc device, particularly for high current output, more condensing surface per unit of vapor space from which heat loss is to be absorbed is required in certain spaces within the tank or lower vacuum chamber proper than in other spaces, for example the space within the condensing dome, since more heat loss is to be taken off per unit of space in this certain portion of the lower or tank space, through which the arc discharge passes from cathode to anodes,

than in other regions. It is to be noted that the absorption of these higher heat losses is practi- 5 cally possible only in the region inwhich they arise since they can not be distributed to other regions and there absorbed, unless a high temperature gradient exists between the regions of high losses and of lower losses. Consequently, unless the heat absorbing means is in direct contact with the vapor in the space in which the above mentioned higher heat losses occur a relatively high vapor pressure will build up therein suflicient to cause failure of the vapor as a valve.

In accordance with my invention the above and other difiiculties are overcome by the provision of additional cooling means in that region of the mercury arc device in which the absorption of heat losses is most effective in maintaining the vapor pressure within predetermined narrow limits, this additional cooling means including elements for conducting a cooling medium in the space adjacent the lower wall of the tank and the space adjacent the anode shield openings through which the arc discharge passes from the cathode to the anodes.

My invention will be better understood from the following description when considered in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a crosssectional view of a space discharge device embodying my invention, and Figs. 2 and 3 are curves illustrating the operation of a cooling system in accordance with my invention and of other systems, employed heretofore.

In Fig. l the space discharge device comprises an evacuated receptacle H), a cathode H of vaporizable material such as mercury, and a plurality of anodes I2 of which one only appears in the drawings. The receptacle I 0 includes a tank portion l3 having a side wall [4 and a lower Wall or floor portion [5 concentrically arranged with reference to the cathode H, and a condensing dome Hi. The anodes I2 are arranged within anode housings or shields I! which are mounted in the upper wall of tank [3 near the side wall l4 thereof and which are provided with openings [8 for the arc discharge between cathode and anodes. In order to absorb heat losses from the spaces within tank I3 and dome I 6, cooling jackets I9, 20 are provided through which cooling medium 2! is circulated from any suitable source, and in order to increase the heat loss absorbing surface for the space above cathode II and within dome it coils 22 are mounted ing chamber 25 formed between the central portion of lower wall or floor portion l5 of tank l3 and the upper side of the cathode mounting member 26, through a pipe 21 to the (101122 within dome i5, through the outlet 28 of coil 22 into the jacket 20, and through the outlet 29 of jacket 20 into a pipe (iii. In cooling systems previously incorporated in the space discharge device shown in Fig. l, and in similar space discharge devices, the. cooling medium was discharged from pipe 3% into the extreme lower portion of jacket l9, being preferably connected for this purpose to a pipe 3! coiled around this lower portion of jacket I?) and having a plurality of orifices 32 to distribute the flow of the cooling medium into the jacket and thereby to avoid local overcooling of the wall E5. The cooling liquid wasthen discharged from the upper portion of jacket it) through an outlet pipe 33.

In accordance with my invention, however, an additional heat loss absorbing means is provided for the space adjacent to the floor portion or lower wall 15 and below and adjacent to the openings l8 of the anode shields l'l, this space being that through which the arc discharge from cathode H to anodes i2 passes to the openings in the anode shields. This additional heat loss absorbing means preferably includes a plurality of cooling medium conducting elements such as 1, coilsof pipe 34 preferably of relatively large diameter, certain of these coils, as 35, being mounted adjacent to the lower wall 15 of tank I3 and preferably spaced far enough from this wall to permit passage of vapor between coils and wall, certainothers of the coils as 36 being mounted adjacent to the, side wall l4 andthe open ends of anode shields II. The pipe 30, instead of being connected directly to the lower portion of jacket 59 through the pipe 3i, as above described in connection with circulating, systems heretofore employed in mercury are devices such as shown inrFig. 1, is connected to the bank of coils 34, the cooling medium then circulating through coils 36 and 35, passing from coils 35 into the lower portion of jacket l9 through pipe 3| and out of the upper portion of the jacket into the discharge pipe 33.

It will be seen that the coils 34 constitute floor coils within the tank 13 so arranged as to form 1 a cooling means, in addition to the cooling means provided by the lower portions of the walls of the tank in contact with cooling medium 2i in jacket it, for absorbing heat losses in the space extending along the floor of the tank to and along the side of the tank into the region system for control of the temperature and pres-.

sure within the evacuated receptacle l0 will be more clearly understood by reference to Figs. 2 and 3. The curves shown in these figures relate to the operation. of mercury are devices of the high power type illustrated in Fig. 1, having, for example, a capacity at full load of the order of 3000 kw. at 600 volts, normal load current being approximately 5000 amperes.

Referring particularly to Fig. 2, the curves therein in dotted line indicate in kilowatts the heat losses absorbed by the cooling means in a mercury arc device which is of the type shown in Fig. 1 but which is not provided with the cooling means represented by floor cells. In these dotted curves of Fig. 2 the curve marked Tank shows the gloss taken ofi by cooling water circulating in jacket 18 in contact with the walls or the tank It; the curve marked Dome shows the loss taken off by cooling water circulating in jacket 20 in' contact with the walls of dome l6;

and the curve marked Coils over cathode shows the loss taken off by cooling water circulating in a coil (not shown) similar to dome coil 22 but mounted centrally of receptacle ID in the lower portion of dome l6.

Similarly the curves in full line in Fig. 2 indicate the heat losses in a mercury arc device of the type shown in Fig. 1 provided with cooling jackets I9, 20 and dome coil 22, and, further, with the additional cooling means represented by floor 7 coils 34. The curves in this figure marked To show that in both types of cooling systems above described, i. e., with and without the floor coils 34, considerably more heat loss occurs in the q lower vacuum chamber than in other regions, for example the region within the condensing dome.

Referring to Fig. 3, the curves therein in dotted line indicate in watts the heat loss which must be absorbed per square inch of various cooling areas at different loads: in a mercury arc device similar to that shown in'Fig. -l but not provided with the additional cooling means represented by floor coils 34. Thus the curve marked Vacuum chamber proper indicates the loss required to be absorbed, per square inch of that condensing area which is provided by the walls of tank l3, in order that the loss in kilowatts in this tank region and indicated by dotted curve marked Tank of Fig. 2 may be taken off by the cooling water. The curve in Fig. 3 marked Coils over cathode indicates the watts required to be absorbed, per square inch of the cooling coil similar to coil 22, mounted as above mentioned centrally of the receptacle in the lower portion of the dome, in order to take off the loss indicated by the curve marked Coils over cathode in Fig. 2. The curve in Fig. 3 marked Dome indicates the watts required to be absorbed, per square inch' of the walls of dome H5, in order to take off the loss indicated by the curve marked Dome in Fig. 2.

larly in watts the heat loss which is required to be absorbed by each square inch of different cooling areas, for loads upto full load, in the mercuryarc device shown in Fig.1, and having the above described additional cooling means The curve in Fig. 3 marked To tank and coil indicatesthe loss required to be absorbed, per sq. in. of the combined cooling area provided by the V in the tank space represented by fioor coils 34.

The curves in full line in Fig. 3 indicate simi 765'? walls of tank I3 plus the area provided by the fioor coils 34, in order to take off the loss in kilowatts indicated in the curve marked To tank and coil of Fig. 2. The curve in Fig. 3 marked To dome and coil indicates the loss required to be absorbed per sq. in. of the cooling area provided by the walls of dome H5 in contact with cooling water in jacket 20 and by the dome coils 22, in order to take off the loss in kilowatts indicated in the curve marked To dome and coil of Fig. 2. Since the area of the cooling and condensing surfaces which is sufiicient to maintain the vapor pressure within safe limits in high power mercury are devices of the type herein described is approximately that area which provides one square inch of cooling surface per five watts of heat loss at load, it will be apparent from Figs. 2 and 3 that, in the mercury arc device which is not provided with the floor coils 34 and to which the dotted curves of .these figures relate, the cooling surfaces provided for the absorption of the heat loss shown in kilowatts by the curve marked Tank of Fig. 2 are overloaded. This is evident since the curve marked Vacuum chamber proper of Fig. 3 indicates that even at 5000 amperes load, representing only normal full load, considerably more than five watts per square inch of cooling surface must be absorbed, in the mercury arc device not provided with the floor coils 34, by the tank walls in contact with cooling medium 2| in jacket Hi. This overloading of the cooling surfaces in the tank region results in a rise of vapor pressure, tending to cause failure of the vapor as a valve, in the tank space including that space in the lower portion of the tank which extends adjacent the floor of the tank from the cathode chamber to the region of the lower open ends of the anode housings l i.

This latter space, through which the are disa charge passes from cathode to anodes, is more effective in holding vapor pressure at a predetermined value With load than other spaces, and it is in this space that I provide in accordance with my invention additional heat absorbing means, represented by floor coils 34, sufficient to increase the total cooling surface preferably to double its former value and to lower the heat absorption per unit area of the cooling surfaces to a point well within the required minimum of five watts per sq. in. at 150% load, for example to four watts per sq. in. in the tank space at this load, as shown in curve marked To tank and coil in Fig. 3. This increase in the effective cooling surface in the tank region provided by floor coils 34 correspondingly decreases the heat absorption load imposed on the cooling surfaces in the dome region, the result being a better balance of the heat absorption per unit area in the entire space within the mercury arc device, as indicated by the curves of Fig. 3.

The above described additional cooling means in accordance with my invention, comprising the floor coils 34 mounted in that space which is most effective in controlling the vapor pressure, is particularly effective in condensing out merc'ury from the vapor blast issuing from the oathode and proceeding in the direction of the anodes, mercury being prevented thereby from penetrating to the hot region adjacent the anodes. The condensing surfaces formed by the coils 34 do not, however, appreciably baflle or constrict the arc discharge between cathode and anodes although the arc passes close to these coils, which are mounted a sufiicient distance from the adjoining Walls of tank [3 to permit the latter surfaces to function efficiently as cooling and condensing areas.

Itwill be observed that by the provision of the additional cooling means described herein as comprising the fioor coils 35, mounted in the space in which cooling surfaces of given area are most effective in controlling vapor pressure, a marked increase in rating in a mercury arc device of given dimensions is obtained with a relatively simple and low cost added structure, a comparable increase in rating being obtained in mercury are devices of the usual type only by an increase in the diameter and other dimensions of the evacuated receptacle and by an increase in the length of the arc stream between cathode and anodes with a resulting objectionable increase in the arc drop, this being approximately volt for each inch increase in arc stream length.

It will be observed further that by the provision of the additional cooling means comprising the floor coils 34 danger of failure of the vapor as a valve particularly in the space between cathodes and anodes, wherein the heat loss per unit space is greatest, is minimized or eliminated at loads substantially higher than normal.

What I claim as newand desire to secure by Letters Patent of the United States, is:

1. The combination with a space discharge device including a metal tank, a cathode, a plurality of anodes, a plurality of anode shields each surrounding a different one of said anodes and each being provided with an opening at the lower end thereof adjacent the corresponding anode, a condensing dome mounted on said tank, means to circulate a cooling medium in contact with the walls of said dome and means including cooling coils mounted within said dome to absorb heat losses therein, and means to circulate a cooling medium in contact with said tank to absorb heat losses in the space between said cathode and said anode shield openings through which space passes the arc discharge between said cathode and said' anodes, of auxiliary cooling means including cooling medium conducting elements mounted closely adjacent throughout their entire extent'to the lower wall portion of said tank in said space to increase the absorption of heat losses in said space to a predetermined rate of absorption, whereby the vapor pressure in said space between said cathode and said anode shield openings is maintained at substantially the same value as that of the vapor pressure in said dome.

2. The combination with a space discharge device including a metal tank, a cathode, a plurality of anodes, and means to circulate a cooling medium in contact with the lower wall portion of said tank to absorb heat losses in the space through which the arc passes between said cathode and said anodes, said cooling means providing substantially less than one square inch of cooling area per five watts of heat loss in said space at 150% load, of auxiliary cooling means for said space including cooling coils mounted in said space closely adjacent said lower wall portion and extending to the region closely adjacent to said anodes, the area of the cooling surface of said auxiliary means being such that the total cooling area for said space provides at least one square inch of cooling area per five watts of heat loss at 150% load.

. 70 3. In a space discharge device including an requiring low absorption of heat loss per unit space, the space below said shield ends which constitutes the arc path between anodes and cathode requiring high absorption of heat loss per unit space, cooling means for said spaces including means to circulate cooling medium in contact with the lower side wall and floor portion of said receptacle, said cooling means absorbing said low heat losses in the first-named space without undesirable cooling in said firstnamed space, said cooling means being insufii- 

